Electrophoretic display panel

ABSTRACT

The electrophoretic display panel( 1 ) for displaying a picture and subsequently displaying a subsequent picture has a pixel( 2 ) having an electrophoretic medium ( 5 ) having first and second charged particles ( 6,7 ) and an optical state depending on the positions of the particles ( 6,7 ) in the common region ( 30 ) of the pixel ( 2 ). Furthermore, transition control means are able to control a transition of the first and the second particles ( 6,7 ) being in substantially separated domains of the common region ( 30 ) for displaying the picture to substantially separated domains of the common region ( 30 ) for displaying the subsequent picture. For the display panel ( 1 ) to be able to have an attainable optical state for displaying the subsequent picture which is unequal to the optical state determined by the mixture of the first and second particles ( 6,7 ), even if the particles ( 6,7 ) have substantially equal electrophoretic mobilities, the transition control means are further able to control the first and the second particles ( 6,7 ) to be in substantially separated domains of the common region ( 30 ) during the transition.

The invention relates to an electrophoretic display panel for displayinga picture and subsequently displaying a subsequent picture comprising

-   -   a pixel having        -   an electrophoretic medium comprising first and second            charged particles, the first charged particles having a            first optical property, the second charged particles having            a second optical property different from the first optical            property, the first and the second charged particles being            able to occupy positions in a common region of the pixel,        -   an optical state depending on the positions of the particles            in the common region, and    -   transition control means being able to control a transition of        at least a first number of the first particles and at least a        second number of the second particles being in separate regions        in the common region for displaying the picture to separate        regions in the common region for displaying the subsequent        picture.

The invention also relates to a display device comprising such anelectrophoretic display panel.

The invention further relates to a method of driving such anelectrophoretic display panel.

An embodiment of the electrophoretic display panel of the type mentionedin the opening paragraph is disclosed in U.S. Pat. No. 6,177,921.

Electrophoretic display panels in general are based on the motion ofcharged, usually colored particles under the influence of an electricfield between electrodes. With these display panels, dark or coloredcharacters can be imaged on a light or colored background, and viceversa. Electrophoretic display panels are therefore notably used indisplay devices taking over the function of paper, referred to as “paperwhite” applications, e.g. electronic newspapers and electronic diaries.

The disclosed electrophoretic display panel is a color display panel.The pixel has a transparent electrode at the side facing the viewer, anelectrode at the side facing away from the viewer, multiple species ofcharged particles in a clear, dispersing fluid between the electrodes.Each species of particles has different optical properties and possessesdifferent electrophoretic mobilities from the other species: e.g. redparticles and blue particles, wherein the magnitude of the electricmobility of the red particles, on average, exceeds the electrophoreticability of the blue particles, on average. Consider the pixel having ablue color for displaying the picture. The pixel having a blue colorresults from the blue particles being nearer to the electrode at theside facing the viewer than the red particles. The picture is updated,resulting in the pixel having e.g. a red color for displaying thesubsequent picture, as follows. All the particles are attracted to theelectrode at the side facing away from viewer by applying an electricfield in the appropriate direction. The electric field should be appliedto the pixel long enough to attract even the more slowly moving blueparticles. Then the electric field is reversed just long enough to allowthe red particles to migrate towards the electrode at the side facingthe viewer. The blue particles will also move in the reversed electricfield, but they will not move as fast as the red particles and thus willbe obscured by the red particles.

The amount of time for which the applied electric field must be reverseddepends on the relative electrophoretic mobilities of the particles andthe strength of the applied electric field. If the picture is updatedtowards the pixel having a blue color for displaying the subsequentpicture the updating is as follows. After the particles are attracted tothe electrode at the side facing away from viewer the electric field isreversed just long enough to allow the red and blue particles to migratetowards the electrode at the side facing the viewer. The electric fieldis then reversed a second time and the red particles moving faster thanthe blue particles leave the blue particles exposed to the viewpoint.Therefore, the optical states attainable for the pixel for displayingthe subsequent picture are red and blue. However, if the particles havesubstantially equal electrophoretic mobilities, only one optical state,being the optical state determined by the mixture of the first andsecond particles, is attainable for the pixel for displaying thesubsequent picture.

It is an object of the invention to provide a display panel of the kindmentioned in the opening paragraph which is able to have an attainableoptical state for displaying the subsequent picture which is unequal tothe optical state determined by the mixture of the first and the secondparticles, even if the particles have substantially equalelectrophoretic mobilities.

The object is thereby achieved that the transition control means arefurther able to control the first number of the first particles and thesecond number of the second particles to be in separate regions in thecommon region during the transition.

As a result, the first number of the first particles and the secondnumber of the second particles are not only in unmixed states fordisplaying the picture, but the particles are held in unmixed statesalso during picture update and are therefore able to reach unmixedstates for displaying the subsequent picture. Therefore, the process ofmixing and subsequently unmixing the first number of the first particlesand the second number of the second particles during picture updatetaking place in the disclosed electrophoretic display panel, is omittedduring picture update in the display panel according to the invention.As a result, the picture update process in the display panel accordingto the invention is independent from differences in electrophoreticmobilities of the first and the second particles. Furthermore, as thefirst number of the first particles and the second number of the secondparticles are brought from separate regions in the common region fordisplaying the picture via separate regions in the common region toseparate regions in the common region for displaying the subsequentpicture, tile optical state for displaying the subsequent picture isunequal to the optical state determined by the mixture of the first andsecond particles.

In an embodiment the transition control means are able to control thetransition of the first and the second particles being in substantiallyseparate regions in the common region for displaying the picture tosubstantially separate regions in the common region for displaying thesubsequent picture, and the transition control means are further able tocontrol the first and the second particles to be in substantiallyseparate regions in the common region during the transition.

As on an atomic/molecular scale two particles always have non-equalpositions, it is clear that substantially separate regions only have ameaning from a macroscopic point of view. First and second particles arein substantially separate regions if e.g. the envelope macroscopicallysurrounding the first particles is substantially non-coinciding with theenvelope macroscopically surrounding the second particles.

In an embodiment

-   -   the common region comprises at least three substantially        separate regions, at least one of which is unoccupied,    -   the transition control means comprise:        -   electrodes for receiving potentials, each one of the            electrodes being associated with a substantially separate            region, and        -   drive means being able to control the potentials to control            the transition of the first and the second particles being            in separate ones of the substantially separate regions for            displaying the picture to separate ones of the substantially            separate regions for displaying the subsequent picture, and    -   the transition comprises a sub-transition wherein a member of a        list having as members a collection of the first particles and a        collection of the second particles is brought from the member's        substantially separate region to one of the substantially empty        separate regions. Furthermore, the transition may also comprise        a number of such sub-transitions. Then the movement and position        of the particles depends on the electric field distribution. As        the electric field distribution depends on the potential        differences and the geometry of the electrodes, the combination        of the geometry of the electrodes and the potential differences        are chosen such that the particles can be brought from        substantially separate regions for displaying the picture via        substantially separate regions during picture update towards        substantially separate regions for displaying the subsequent        picture. Furthermore, the substantially separate regions as well        as the sub-transitions are well-defined.

In a variation on the embodiment

-   -   a first one of the substantially separate regions provides a        first reservoir for the first particles substantially        non-contributing to the optical state of the pixel, and    -   a second one of the substantially separate regions provides a        second reservoir for the second particles substantially        non-contributing to the optical state of the pixel,    -   a third one of the substantially separate regions substantially        contributes to the optical state of the pixel, and    -   the transition comprises:        -   a first sub-transition wherein the member being in the third            one of the substantially separate regions for displaying the            picture is brought to the member's reservoir, and            subsequently        -   a second sub-transition wherein one of the members is            brought from the member's reservoir to the third one of the            substantially separate regions for displaying the subsequent            picture.

Then the geometry is relatively simple and the driving scheme canrelatively simply be implemented. Furthermore, the pixel has at leastthree attainable optical states, being the optical states determined by

-   1) the first particles being in the third one of the substantially    separate regions,-   2) the second particles being in the third one of the substantially    separate regions, and-   3) none of the first and the second particles being in the third one    of the substantially separate regions.

Furthermore, optical states intermediate between optical states 1) and3) are also attainable. This can e.g. be realized if in the transitiononly a limited number of the first particles is brought to the third oneof the substantially separate regions. Furthermore, optical statesintermediate between optical states 2) and 3) are also attainable. Thiscan e.g. be realized if in the transition only a limited number of thesecond particles is brought to the third one of the substantiallyseparate regions.

In another variation on the embodiment

-   -   a first one of the substantially separate regions provides a        first reservoir for the first particles substantially        noncontributing to the optical state of the pixel, and    -   a second one of the substantially separate regions provides a        second reservoir for the second particles substantially        non-contributing to the optical state of the pixel,    -   a third one and a fourth one of the substantially separate        regions each substantially contribute to the optical state of        the pixel, and    -   the transition comprises:        -   a first sub-transition wherein the members being in the            third one and the fourth one of the substantially separate            regions for displaying the picture are brought to their            respective reservoirs, and subsequently        -   a second sub-transition wherein the members are brought from            their respective reservoirs to the third one and the fourth            one of the substantially separate regions for displaying the            subsequent picture.

Then the geometry is relatively simple and the driving scheme canrelatively simply be implemented. Furthermore, the pixel has at leastnine attainable optical states, being the optical states determined by

-   1) the first particles being in the third and the fourth one of the    substantially separate regions,-   2) the first particles being in the third one of the substantially    separate regions and none of the first and the second particles    being in the fourth one of the substantially separate regions,-   3) the first particles being in the fourth one of the substantially    separate regions and none of the first and the second particles    being in the third one of the substantially separate regions,-   4) the second particles being in the third one and the fourth one of    the substantially separate regions,-   5) the second particles being in the third one of the substantially    separate regions and none of the first and the second particles    being in the fourth one of the substantially separate regions,-   6) the second particles being in the fourth one of the substantially    separate regions and none of the first and tile second particles    being in the third one of the substantially separate regions,-   7) the first particles being in the third one of the substantially    separate regions and the second particles being in the fourth one of    the substantially separate regions,-   8) the second particles being in the third one of the substantially    separate regions and the first particles being in the fourth one of    the substantially separate regions, and-   9) none of the first and the second particles being in the third one    and the fourth one of the substantially separate regions    Similarly to the previous embodiment, intermediate optical states    are also attainable.

In another variation on the embodiment

-   -   a first one of the substantially separate regions provides a        first reservoir for the first particles substantially        non-contributing to the optical state of the pixel, and    -   a second one of the substantially separate regions provides a        second reservoir for the second particles substantially        non-contributing to the optical state of the pixel,    -   a third one and a fourth one of the substantially separate        regions each substantially contribute to the optical state of        the pixel, and    -   the transition comprises:        -   a first sub-transition wherein the members being in the            third one and the fourth one of the substantially separate            regions for displaying the picture that will be absent in            the third one and the fourth one of the substantially            separate regions for displaying the subsequent picture are            brought to their respective reservoirs, and subsequently        -   a second sub-transition wherein the members which are absent            in the third one and the fourth one of the substantially            separate regions for displaying the picture that have to be            present in the third one and the fourth one of the            substantially separate regions for displaying the subsequent            picture are brought from their respective reservoirs to the            third one and/or the fourth one of the substantially            separate regions for displaying the subsequent picture.            In this way unnecessary movement of particles is reduced,            whereas, furthermore, the optical state during picture            update may be optically closer to the optical state of the            subsequent picture than in the previous variation on the            embodiment thereby providing a smoother picture update.

In yet another variation on the embodiment

-   -   the pixel has a viewing surface for being viewed by a viewer,    -   the electrodes have substantially flat surfaces facing the        particles, and    -   the surfaces are substantially parallel to the viewing surface.

Then the geometry of the electrodes and surfaces of the electrodes canrelatively simply be manufactured. If, furthermore, the surfaces of theelectrodes are present in a substantially flat plane, the manufacturingprocess of the electrodes is further simplified.

In still another variation on the embodiment

-   -   the pixel has a viewing surface for being viewed by a viewer,    -   the electrodes have substantially flat surfaces facing the        particles,    -   the surfaces of the electrodes being associated with        substantially separate regions that are substantially        contributing to the optical state of the pixel are substantially        parallel to the viewing surface, and    -   the surfaces of the electrodes being associated with        substantially separate regions that are substantially        non-contributing to the optical state of the pixel are        substantially perpendicular to the viewing surface.

This results in a more compact layout of the pixel.

In still another variation on the embodiment

-   -   a first one of the substantially separate regions provides a        first reservoir for the first particles,    -   a second one of the substantially separate regions provides a        second reservoir for the second particles, and    -   the display panel further comprises first decoupling means to        reduce the influence of the potential of the electrode        associated with the first reservoir on the position of the        second particles.        If, furthermore, the display panel further comprises second        decoupling means to reduce the influence of the potential of the        electrode associated with the second reservoir on the position        of the first particles. Then the positions of the first and        second particles can relatively accurate be determined by the        potentials.

In a variation on the embodiment the first and the second decouplingmeans are realised by the electrophoretic medium comprising a hyseresiseffect. The electrophoretic medium comprises a hysteresis effect if thefollowing holds: if the electrophoretic medium is brought from a firststate into a second state by applying a potential difference, reversalof the applied potential difference does not bring the medium back fromthe second state into the first state. Then the movement and position ofthe particles also depends on the history of the potential differences.This hysteresis effect can be used as decoupling means.

In another variation on the embodiment the first and the seconddecoupling means comprise a first and a second gate electrode forreceiving a first and a second gate potential, the first and the secondgate electrode being present between the electrodes associated with thefirst and the second reservoir. It is advantageous if, furthermore, thefirst gate electrode is present between the electrode associated withthe first reservoir and the electrode associated with a third one of thesubstantially separate regions and the second gate electrode is presentbetween the electrode associated with the second reservoir and theelectrode associated with the third one of the substantially separateregions. It is advantageous if, furthermore, in operation, thepotentials of the electrodes associated with the first and the secondreservoir and the potential of the electrode associated with the thirdone of the substantially separate regions are substantially constant intime. Then the electrodes associated with the first and the secondreservoir and the electrode associated with the third one of thesubstantially separate regions are passive components during imageupdate, whereas the transition is controlled by the first and the secondgate potential. As a result, the design of the display panel is lesscomplicated.

In yet another variation on the embodiment the first and the seconddecoupling means comprise a first particles repulsive layer presentbetween the electrode associated with the first reservoir and theelectrode associated with a third one of the substantially separateregions, and a second particles repulsive layer present between theelectrode associated with the second reservoir and the electrodeassociated with the third one of the substantially separate regions.

In still another variation on the embodiment the first and the seconddecoupling means comprise a first membrane through which a passage ofthe first particles is determined by a first threshold, the firstmembrane being present between the electrode associated with the firstreservoir and the electrode associated with a third one of thesubstantially separate regions, and a second membrane through which apassage of the second particles is determined by a second threshold, thesecond membrane being present between the electrode associated with thesecond reservoir and the electrode associated with the third one of thesubstantially separate regions.

In another embodiment, the display panel is an active matrix displaypanel.

Another aspect of the invention provides a display device comprising anelectophoretic display panel as claimed in claim 18.

Yet another aspect of the invention provides a method of driving anelectrophoretic display panel as claimed in claim 19.

In an embodiment the method comprises controlling the transition of thefirst and the second particles from substantially separate regions inthe common region for displaying the picture via substantially separateregions in the common region to substantially separate regions in thecommon region for displaying the subsequent picture.

These and other aspects of the display panel of the invention will befurther elucidated and described with reference to the drawings, inwhich:

FIG. 1 shows diagrammatically a front view of an embodiment of thedisplay panel;

FIG. 2 shows diagrammatically a cross-sectional view along II-II in FIG.1;

FIG. 3 shows diagrammatically some details of FIG. 2;

FIG. 4 shows diagrammatically cross-sectional view along IV-IV in FIG.3, the cross-sectional view representing a layout of the electrodes of apixel;

FIGS. 5-11 show diagrammatically other layouts of electrodes of a pixel;

FIG. 12 shows diagrammatically a cross-sectional view along II-II inFIG. 1 of another embodiment of the display panel;

FIG. 13 show diagrammatically a layout of electrodes of a pixel; and

FIG. 14 shows diagrammatically a cross-sectional view along II-II inFIG. 1 of another embodiment of the display panel.

In all the Figures corresponding parts are referenced to by the samereference numerals.

FIGS. 1, 2, 3 and 4 show an example of the display panel 1 having afirst substrate 8, a second transparent opposed substrate 9 and aplurality of pixels 2. Preferably, the pixels 2 are arranged alongsubstantially straight lines in a two-dimensional structure. Otherarrangements of the pixels 2 are alternatively possible, e.g. ahoneycomb arrangement. In an active matrix embodiment, the pixels 2 mayfurther comprise switching electronics, for example, thin filmtransistors (TFTs), diodes, MIM devices or the like.

An electrophoretic medium 5, having first charged particles 6 and secondcharged particles 7 in a fluid, is present between the substrates 8,9.Electrophoretic media 5 are known per se from e.g. U.S. 2002/0180688 andcan e.g. be obtained from E Ink Corporation. The first charged particles6 have a first optical property. The second charged particles 7 have asecond optical property different from the first optical property. Thefirst particles 6 may have any color, whereas the second particles 7 mayhave any color different from the color of the first particles 6. Thecolor of the first particles 6 is for instance red, green, blue, yellow,cyan, magenta, white or black. Preferably, the first and secondparticles 6,7 have different basic colors, e.g. the first particles 6being red and second particles 7 being green. The first and the secondparticles 6,7 are able to occupy positions in a common region 30 of thepixel 2. The optical state of a pixel 2 depends on the positions of theparticles 6,7 in the common region 30. The transition control means areable to control a transition of the first and the second particles 6,7being in substantially separate regions in the common region 30 fordisplaying the picture to substantially separate regions in the commonregion 30 for displaying the subsequent picture. The transition controlmeans are further able to control the first and the second particles 6,7to be in substantially separate regions in the common region 30 duringthe transition.

The configuration of FIG. 2 is shown in some detail in FIG. 3. The pixel2 has a viewing surface 91 for being viewed by a viewer. The commonregion 30 has three substantially separate regions 20,21,25. Thetransition control means has electrodes 10,11,15 for receivingpotentials. Each one of the electrodes 10,11,15 is associated with arespective substantially separate region 20,21,25. In this case, eachone of the electrodes 10,11,15 has a substantially flat surface110,111,115 facing the particles 6,7 and the viewing surface 91.Furthermore, the surfaces 110,11,115 of the electrodes 10,11,15 arepresent in a substantially flat plane. The transition control means hasdrive means 100 able to control the potentials to control the transitionof the first and the second particles 6,7 being in separate ones of thesubstantially separate regions 20,21,25 for displaying the picture toseparate ones of the substantially separate regions 20,21,25 fordisplaying the subsequent picture. Furthermore, the transition comprisesa number of sub-transitions wherein in each sub-transition a member ofthe first and the second particles 6,7 is brought from the member'ssubstantially separate region to one of the substantially empty separateregions.

In FIG. 4 a layout of the electrodes 10,11,15 is shown. In this example,the substantially separate regions 20,21,25 contribute respectively 25%,25% and 50% to the optical state of the pixel 2. This may e.g. beachieved by the electrodes 10,11, 15 having surface areas at ratios of1:2:1 as seen by an observer. Consider the fluid to be transparent, thefirst and second particles 6,7 to be negatively charged and the firstparticles 6 to have a red color, denoted by R, and the second particles7 to have a green color, denoted by G. Furthermore, the electrodes10,11,15 are blue, denoted by B. Consider the pixel layout of FIG. 4. Asan example, for displaying the picture, the red particles 6 are insubstantially separate region 20 near the surface 110 of electrode 10,and the green particles 7 are in substantially separate region 21 nearthe surface 111 of electrode 11, whereas substantially no particles 6,7are in substantially separate region 25. The electrodes 10,11,15 haverespective potentials of e.g. 10 Volts, 10 Volts and 0 Volts. Theoptical state of the pixel 2 for displaying the picture is denoted by ¼R ¼ G ½ B, i.e. the optical state of the pixel 2 is an average of 25%red, 25% green and 50% blue. Consider the optical state of the pixel 2for displaying the subsequent picture to be ¼ R ½ G ¼ B. To obtain thisoptical state, the electrodes 10,11,15 receive respective potentials ofe.g. 10 Volts, 0 Volts, and 10 Volts from the drive means 100. Thecombination of electrode geometries and potentials is chosen such thatnear the surface 110 of electrode 10 substantially no electric field ispresent and between electrodes 11 and 15 an electric field is present inthe appropriate direction. As a result, the red particles 6 remainpresent near the surface 110 of electrode 10 in substantially separateregion 20 and the green particles 7 are brought from their position nearthe surface 111 of electrode 11 to a position near the surface 115 ofelectrode 15 in substantially separate region 25. Then the optical stateof the pixel 2 for displaying the subsequent picture is ¼ R ½ G ¼ B.

Note that the pixel 2 has at least three achievable optical states: ¼ R¼ G ½ B, ¼ R ½ G ¼ B and ½ R ¼ G ¼ B. If the optical state of the pixel2 for displaying the picture is ¼ R ½ G ¼ B and the optical state of thepixel 2 for displaying the subsequent picture is ½ R ¼ G ¼ B then thetransition is somewhat more complicated. For displaying the picture, theelectrodes 10,11,15 have respective voltages 10 Volts, 0 Volts, 10Volts. For achieving the first sub-transition, the electrodes 10,11,15receive respective potentials 10 Volts, 10 Volts and 0 Volts from thedrive means 100. As a result, the red particles 6 remain present nearthe surface 110 of electrode 10 in substantially separate region 20 andthe green particles 7 are brought from their position near the surface115 of electrode 15 to a position near the surface 111 of electrode 11in substantially separate region 21. Subsequently, for achieving thesecond sub-transition, the electrodes 10,11,15 receive respectivepotentials 0 Volts, 10 Volts and 10 Volts from the drive means 100. As aconsequence of these potentials, the green particles 7 remain presentnear the surface 111 of electrode 11 in substantially separate region 21and the red particles 6 are brought from their position near the surface110 of electrode 10 to a position near the surface 115 of electrode 15in substantially separate region 25. Then the optical state of the pixel2 for displaying the subsequent picture is ½ R ¼ G ¼ B.

In FIG. 5 a layout of the electrodes 10,11,15 in another embodiment ofthe pixel 2 is shown. In this example, substantially separate region 20provides a first reservoir for the red particles 6 and is substantiallynon-contributing to the optical state of the pixel 2 and substantiallyseparate-region 21 provides a second reservoir for the green particles 7and is substantially non-contributing to the optical state of the pixel2. Substantially separate region 25 substantially determines the opticalstate of the pixel 2. This is achieved by the surface area of electrode15 as seen by an observer being at least one order of magnitude largerthan the surface areas of electrodes 10 and 11 as seen by an observer.Another way of achieving this is by shielding electrodes 10 and 11 fromthe observer by e.g. having a light absorbing layer between theelectrodes 10 and 11 the observer. The driving scheme for changing theoptical state is similar to the driving scheme of the pixel 2 of FIG. 4.Note that the pixel 2 has at least three achievable optical statesrelated to the three basic colors: R (red particles 6 near the surface115 of electrode 15), G (green particles 7 near the surface 115 ofelectrode 15) and B (blue color of that surface 115 of electrode 15, asno red and green particles 6,7 are near the surface 115 of electrode15). Furthermore, optical states intermediate between the three basiscolors are also attainable. This can e.g. be realized if in thetransition only a limited number of the red particles 6 or the greenparticles 7 are brought near the surface 115 of electrode 15.

Many other layouts of the electrodes 10,11,15 of the pixel 2 arepossible, see e.g. the layouts shown in FIGS. 6 and 7.

In another embodiment, the first, second, third and fourth particles6,7,40,41 are negatively charged and the particles 6,7,40,41 are red,green, blue and white, denoted by W, respectively. The common region 30has five substantially separate regions 20,21,22,23,25. The transitioncontrol means has electrodes 10,11,12,13,15 for receiving potentials.Each one of the electrodes 10,11,12,13,15 is associated with arespective substantially separate region 20,21,22,23,25. In this case,each one of the electrodes 10,11,12,13,15 has a flat surface110,111,112,115 facing the second substrate 9. The layout of the pixel 2is shown in FIG. 8. The substantially separate regions 20,21,22,23provide a first reservoir for the red particles 6, a second reservoirfor the green particles 7, a third reservoir for the blue particles 40,and a fourth reservoir for the white particles 41, respectively, and aresubstantially non-contributing to the optical state of the pixel 2. Thesubstantially separate region 25 substantially determines the opticalstate or the pixel 2. Electrode 15 is black.

The pixel has five achievable optical states: Black, R, G, B and W. As aresult, the display is able to provide an accurate color picture. As anexample, for displaying the picture, the red particles 6 are insubstantially separate region 20 near the surface 110 of electrode 10,the green particles 7 are in substantially separate region 21 near thesurface 111 of electrode 11, the blue particles 40 are in substantiallyseparate region 22 near the surface 112 of electrode 12, the whiteparticles 41 are in substantially separate region 25 near the surface115 of electrode 15, whereas substantially no particles 6,7,40,41 are insubstantially separate region 23 near the surface 113 of electrode 13.The electrodes 10,11,12,13,15 have respective potentials 10 Volts, 10Volts, 10 Volts, 0 Volts and 10 Volts. The optical state of the pixel 2for displaying the picture is W. Consider the optical state of the pixel2 for displaying the subsequent picture to be R. For achieving the firstsub-transition, the electrodes 10,11,12,13,15 receive respectivepotentials 0 Volts, 0 Volts, 0 Volts, 10 Volts and 0 Volts from thedrive means 100. As a result, the red, green and blue particles 6,7,40remain present near the surface of their respective electrodes 10,11,12,whereas the white particles 41 are brought from their position near thesurface 115 of electrode 15 to a position near the surface 114 ofelectrode 14 in substantially separate region 24. Subsequently, forachieving the second sub-transition, the electrodes 10,11,12,13,15receive respective potentials 0 Volts, 10 Volts, 10 Volts, 10 Volts and10 Volts from the drive means 100. As a consequence of these potentials,the green, blue and white particles 7,40,41 remain present near thesurface of their respective electrodes 11,12,13 and the red particles 6are brought from their position near the surface 110 of electrode 10 toa position near the surface 115 of electrode 15 in substantiallyseparate region 25. Then the optical state of the pixel 2 for displayingthe subsequent picture is R.

Many other layouts of the electrodes 10,11,12,13,15 of the pixel 2 arepossible, see e.g. the layouts shown in FIGS. 9 and 10.

As another example, consider the first particles 6 to be negativelycharged and having a red color, and the second particles 7 to bepositively charged and having a green color. The common region 30 hasfour substantially separate regions 20,21,25,26. The transition controlmeans has electrodes 10,11,15,16 for receiving potentials. Each one ofthe electrodes 10,11,15,16 is associated with a respective substantiallyseparate region 20,21,25,26. In this case, each one of the electrodes10,11,15,16 has a flat surface 110,111, 115,116 facing the secondsubstrate 9. The layout of the pixel 2 is shown in FIG. 11. Thesubstantially separate regions 10 and 11 provide a first reservoir forthe red particles 6 and a second reservoir for the green particles 7,respectively, and are substantially non-contributing to the opticalstate of the pixel 2. The substantially separate regions 25 and 26substantially determine the optical state of the pixel 2; in thisexample, each region 25 and 26 contributes 50% to the optical state ofthe pixel 2. Electrodes 15 and 16 are blue. As an example, fordisplaying the picture, the red particles 6 are in substantiallyseparate region 20 near the surface 110 of electrode 10 and the greenparticles 7 are in substantially separate region 21 near the surface 111of electrode 11, whereas substantially no particles 6,7 are insubstantially separate regions 25 and 26 near the surfaces 116,116 ofelectrodes 15 and 16. The electrodes 10,11,15,16 have respectivepotentials 10 Volts, −10 Volts, 0 Volts and 0 Volts. Then the opticalstate of the pixel 2 for displaying the picture is B. To obtain anoptical state of the pixel 2 for displaying the subsequent picture beingR, the electrodes 10,11,15,16 receive respective potentials 0 Volts, −10Volts, 10 and 10 Volts from the drive means 100. As a consequence ofthese potentials, the red particles 6 are brought from their positionnear the surface 110 of electrode 10 to a position near the surfaces115,116 of electrodes 15 and 16 in substantially separate regions 25 and26 and the green particles 7 remain present near the surface 111 ofelectrode 11 in substantially separate region 21. Then the optical stateof the pixel 2 for displaying the subsequent picture is R.

Note that to obtain an optical state of the pixel 2 for displaying thesubsequent picture being ½ R ½ B, the electrodes 10,11,15,16 receiverespective potentials 0 Volts, −10 Volts, 10 and 0 Volts. As aconsequence of these potentials, the red particles 6 are brought fromtheir position near the surface 110 of electrode 10 to a position nearthe surface 115 of electrode 15 in substantially separate region 25 andthe green particles 7 remain present near the surface 111 of electrode11 in substantially separate region 21.

Furthermore, note that an optical state of the pixel 2 for displayingthe subsequent picture being ½ R ½ G is also achievable. To obtain thisoptical state the electrodes 10,11,15,16 receive respective potentials 0Volts, 0 Volts, 10 and −10 Volts. As a consequence of these potentials,the red particles 6 are brought from their position near the surface 110of electrode 10 to a position near the surface 115 of electrode 15 insubstantially separate region 25 and the green particles 7 are broughtfrom their position near the surface 111 of electrode 11 to a positionnear the surface 116 of electrode 16 in substantially separate region26.

If the optical state of the pixel 2 for displaying the picture is R andthe optical state of the pixel 2 for displaying the subsequent pictureis ½ R ½ G, at least two different transitions are possible.

The first transition is as follows. For displaying the picture, theelectrodes 10,11,15,16 have respective potentials 0 Volts, −10 Volts, 10and 10 Volts. For achieving the first sub-transition, the electrodes10,11,15,16 receive respective potentials 10 Volts, −10 Volts, 0 Voltsand 0 Volts from the drive means 100. As a result, the red particles 6are brought from their position near the surfaces 115,116 of electrodes15 and 16 to a position near the surface 110 of electrode 10 insubstantially separate region 20 and the green particles 7 remainpresent near the surface 111 of electrode 11 in substantially separateregion 21. This first sub-transition can be considered as a resetting ofthe optical state of the pixel 2. Subsequently, for achieving the secondsub-transition, the electrodes 10,11,15,16 receive respective potentials0 Volts, 0 Volts, 10 Volts and −10 Volts from the drive means 100. As aconsequence of these potentials, the red particles 6 are brought fromtheir position near the surface 110 of electrode 10 to a position nearthe surface 115 of electrode 15 in substantially separate region 25 andthe green particles 7 are brought from their position near the surface111 of electrode 11 to a position near the surface 116 of electrode 16in substantially separate region 26. Then the optical state of the pixel2 for displaying the subsequent picture is ½ R ½ G.

The second transition is as follows. For displaying the picture, theelectrodes 10,11,15,16 have respective potentials 0 Volts, −10 Volts, 10and 10 Volts. For achieving the first sub-transition, the electrodes10,11,15,16 receive respective potentials 0 Volts, −10 Volts, 10 Voltsand 0 Volts from the drive means 100. As a result, the red particles 6are brought from their position near the surfaces 115,116 of electrodes15 and 16 to a position near the surface 115 of electrode 15 insubstantially separate region 25 and the green particles 7 remainpresent near the surface 111 of electrode 11 in substantially separateregion 21. Subsequently, for achieving the second sub-transition, theelectrodes 10,11,15,16 receive respective potentials 0 Volts, 0 Volts,10 Volts and −10 Volts from the drive means 100. As a consequence ofthese potentials, the red particles 6 remain present near the surface115 of electrode 15 in substantially separate region 25 and the greenparticles 7 are brought from their position near the surface 111 ofelectrode 11 to a position near the surface 116 of electrode 16 insubstantially separate region 26. Then the optical state of the pixel 2for displaying the subsequent picture is ½ R ½ G. Note that the pixel 2has 6 achievable optical states: R, G, B, ½ R ½ G, ½ R ½ B, ½ G ½ B.

In FIG. 12 the layout of the electrodes 10,11,15 in another embodimentof the pixel 2 is shown. In this example, the pixel 2 has a viewingsurface 91 for being viewed by a viewer and the electrodes 10,11,15 havesubstantially flat surfaces 110, 111, 115 facing the particles 6,7.Surface 110 of electrode 10 being associated with substantially separateregion 20 that is substantially non-contributing to the optical state ofthe pixel 2 is substantially perpendicular to the viewing surface 91.Furthermore, surface 111 of electrode 11 being associated withsubstantially separate region 21 that is substantially non-contributingto the optical state of the pixel 2 is substantially perpendicular tothe viewing surface 91. Furthermore, surface 115 of electrode 15 beingassociated with substantially separate region 25 that is substantiallycontributing to the optical state of the pixel 2 is substantiallyparallel to the viewing surface 91.

In another embodiment, electrode 10 is associated with substantiallyseparate region 20 which provides a first reservoir for the negativelycharged first particles 6, electrode 11 is associated with substantiallyseparate region 21 which provides a second reservoir for the negativelycharged second particles 7, and the electrophoretic medium has ahysteresis effect. An example of the layout of the pixel 2 is shown inFIG. 4. As an example, for displaying the picture, the red particles 6are in substantially separate region 20 near the surface 100 ofelectrode 10, and the green particles 7 are in substantially separateregion 21 near the surface 111 of electrode 11, whereas substantially noparticles 6,7 are in substantially separate region 25. Furthermore, theelectrodes 10,11,15 are blue. The electrodes 10,11,15 have respectivepotentials of e.g. 10 Volts, 10 Volts and 0 Volts. The optical state ofthe pixel 2 for displaying the picture is ¼ R ¼ G ½ B. Consider theoptical state of the pixel 2 to be obtained for displaying thesubsequent picture to be ¼ R ½ G ¼ B. To obtain this optical state, theelectrodes 10,11,15 receive respective potentials of e.g. 10 Volts, 0Volts, and 10 Volts from the drive means 100. As a result, the redparticles 6 remain present near the surface 110 of electrode 10 insubstantially separate region 20 and the green particles 7 are broughtfrom their position near the surface 111 of electrode 11 to a positionnear the surface 115 of electrode 15 in substantially separate region25. Then the optical state of the pixel 2 for displaying the subsequentpicture is ¼ R ½ G ¼ B. As a consequence of the electrophoretic mediumhaving a hysteresis effect the substantially separate regions have areduced overlap compared to the substantially separate regions in casethe electrophoretic medium is ideal. Furthermore, because of theelectrophoretic medium has a hysteresis effect, the potential ofelectrode 15 can be somewhat larger than the potential of electrode 10,e.g. the potential of electrodes 10 and 15 being 10 Volts and 11 Volts,respectively, without substantially changing the position of the redparticles 6 near the surface 110 of electrode 10.

In yet another embodiment, electrode 10 is associated with substantiallyseparate region 20 which provides a first reservoir for the negativelycharged first paricles 6, electrode 11 is associated with substantiallyseparate region 21 which provides a second reservoir for the negativelycharged second particles 7. Furthermore, a first and a second gateelectrode 50,51 for receiving a first and a second gate potential arepresent. The first gate electrode 50 is present between electrode 10 andelectrodes 11 and 15 whereas the second gate electrode 51 is presentbetween electrode 11 and electrodes 10 and 15. An example of the layoutof the pixel 2 is shown in FIG. 13. As an example, for displaying thepicture, the red particles 6 are in substantially separate region 20near the surface 110 of electrode 10, and the green particles 7 are insubstantially separate region 21 near the surface 111 of electrode 11,whereas substantially no particles 6,7 are present in substantiallyseparate region 25. Furthermore, the electrodes 10,11,15 are blue. Inthis example, the substantially separate regions 20,21,25 contributerespectively 25%, 25% and 50% to the optical state of the pixel 2. Theelectrodes 10,11,15,50,51 have respective potentials of e.g. 10 Volts,10 Volts, 0 Volts, −1 Volts and −1 Volts. The optical state of the pixel2 for displaying the picture is denoted by ¼ R ¼ G ½ B. The electrodes10,11,15,50,51 have respective potentials of e.g. 10 Volts, 10 Volts, 15Volts, −1 Volts and −1 Volts. In this example, the first and the secondgate potential of −1 Volts prevent the red particles 6 and the greenparticles 7 from being attracted by electrode 15. Consider the opticalstate of the pixel 2 to be obtained for displaying the subsequentpicture to be ¼ R ½ G ½ B. To obtain this optical state, the electrodes10,11,15,50,51 receive respective potentials of e.g. 10 Volts, 10 Volts,15 Volts, −1 Volts and 0 Volts from the drive means 100. In thisexample, the first gate potential of −1 Volts prevents the red particles6 from being attracted by electrode 15. Furthermore, the second gatepotential of 0 Volts does not prevent the green particles 7 from beingattracted by electrode 15. Other values of the second gate potential,e.g. the range 0 to 10 Volts, can also be used. As a result, the redparticles 6 remain present near the surface 110 of electrode 10 insubstantially separate region 20 and the green particles 7 are broughtfrom their position near the surface 111 of electrode 11 to a positionnear the surface 115 of electrode 15 in substantially separate region25. Then the optical state of the pixel 2 for displaying the subsequentpicture is ¼ R ½ G ¼ B. As a consequence of the red particles 6 aretrapped near the surface 110 of electrode 10 and the green particles 7are trapped near the surface 115 of electrode 15. Therefore, thesubstantially separate regions 20,21,25 have reduced or preferably zerooverlap compared to the substantially separate regions 20,21,25 in casethe gate electrodes were absent.

Many other layouts of the electrodes 10,11,15,50,51 of the pixel 2 arepossible, see e.g. the layout shown in FIG. 14.

In the pixel 2 the particles are in substantially separate regions. Thiscan relatively easy be achieved during manufacture in the following way.Consider that the electrode structure has already been manufactured andthe different particles have to be filled in the substantially separateregions. As an example, the geometry of the electrodes of the pixel 2 asshown in FIG. 8 is used. Consider the red, green, blue and whiteparticles 6,7,40,41 to be positively charged. The order in which theparticles 6,7,40,41 are being filled is arbitrary.

In this example, firstly, the red particles 6 are being filled. Toachieve this, the electrodes 10,11,12,13,15 receive respectivepotentials 10 Volts, 0 Volts, 0 Volts, 0 Volts and 0 Volts from thedrive means 100 and the container from which the red particles 6 arebeing filled has a potential of e.g. −5 Volts. The exit of the containeris arranged near the pixel 2 to achieve that, as a consequence of thepotentials, the red particles 6 exit from the container and occupy aposition near the surface 110 of electrode 10 in substantially separateregion 20.

Secondly, the green particles 7 are being filled. To achieve this, theelectrodes 10,11,12,13,15 receive respective potentials 0 Volts, 10Volts, 0 Volts, 0 Volts and 0 Volts from the drive means 100 and thecontainer from which the green particles 7 are being filled has apotential of −5 Volts. The exit of the container is arranged near thepixel 2 to achieve that, as a consequence of the potentials the greenparticles 7 exit from the container and occupy a position near thesurface 111 of electrode 11 in substantially separate region 21.Furthermore, as a consequence of the potentials, the red particles 6that already have been filled remain at their position.

Thirdly, the blue particles 40 are being filled. To achieve this, theelectrodes 10,11,12,13,15 receive respective potentials 0 Volts, 0Volts, 10 Volts, 0 Volts and 0 Volts from the drive means 100 and thecontainer from which the blue particles 40 are being filled has apotential of −5 Volts. The exit of the container is arranged near thepixel 2 to achieve that, as a consequence of the potentials, the blueparticles 40 exit from the container and occupy a position near thesurface 112 of electrode 12 in substantially separate region 22.Furthermore, as a consequence of the potentials, the red and greenparticles 6,7 that already have been filled remain at their respectivepositions.

Fourthly, the white particles 41 are being filled. To achieve this, theelectrodes 10,11,12,13,15 receive respective potentials 0 Volts, 0Volts, 0 Volts, 10 Volts and 0 Volts from the drive means 100 and thecontainer from which the white particles 41 are being filled has apotential of −5 Volts. The exit of the container is arranged near thepixel 2 to achieve that, as a consequence of the potentials, the whiteparticles 41 exit from the container and occupy a position near thesurface 113 of electrode 13 in substantially separate region 23.

Furthermore, as a consequence of the potentials, the red, green and blueparticles 6,7,40 that already have been filled remain at theirrespective positions. As a result the pixel 2 has four differentparticles 6,7,40,41 in substantially separate regions 20,21,22,23,whereas substantially no particles 6,7,40,41 are present insubstantially separate region 24.

1. An electrophoretic display panel for displaying a picture andsubsequently displaying a subsequent picture comprising: a pixel havingan electrophoretic medium comprising first and second charged particles,the first charged particles having a first optical property, the secondcharged particles having a second optical property different from thefirst optical property, the first and the second charged particles beingable to occupy positions in a common region of the pixel, the commonregion comprising at least three substantially separate sub-regions; anoptical state depending on the positions of the particles in the commonregion, and transition control means comprising: electrodes forreceiving potentials, each one of the electrodes being associated withone of the sub-regions, and drive means being arranged to control thepotentials to control the transition of at least a first number of thefirst particles and at least a second number of the second particlesbeing in respective separate sub-regions of the common region fordisplaying the picture, to separate sub-regions of the common region fordisplaying the subsequent picture, wherein the transition control meansare further arranged to control the first number of the first particlesand the second number of the second particles to always be in separatesub-regions of the common region during the transition.
 2. A displaypanel as claimed in claim 1 characterized in that a first one of thesub-regions provides a first reservoir for the first particlessubstantially non-contributing to the optical state of the pixel, and asecond one of the sub-regions provides a second reservoir for the secondparticles substantially non-contributing to the optical state of thepixel, a third one of the sub-regions substantially contributes to theoptical state of the pixel, and the transition comprises: a firstsub-transition wherein the particles in the third sub-region fordisplaying the picture are brought to one of the first and secondsub-regions and subsequently a second sub-transition wherein theparticles of the other of the first and second sub-region are brought tothe third sub-region for displaying the subsequent picture.
 3. A displaypanel as claimed in claim 1 characterized in that a first one of thesub-regions provides a first reservoir for the first particlessubstantially non-contributing to the optical state of the pixel, and asecond one of the sub-regions provides a second reservoir for the secondparticles substantially non-contributing to the optical state of thepixel, a third one and a fourth one of the sub-regions eachsubstantially contribute to the optical state of the pixel, and thetransition comprises: a first sub-transition wherein the particles inthe third and the fourth sub-regions for displaying the picture arebrought to their respective reservoirs, and subsequently a secondsub-transition wherein the particles are brought from their respectivereservoirs to the third one and the fourth sub-regions for displayingthe subsequent picture.
 4. A display panel as claimed in claim 1characterized in that a first one of the sub-regions provides a firstreservoir for the first particles substantially non-contributing to theoptical state of the pixel, and a second one of the sub-regions providesa second reservoir for the second particles substantiallynon-contributing to the optical state of the pixel, a third one and afourth one of the sub-regions each substantially contribute to theoptical state of the pixel, and the transition comprises: a firstsub-transition wherein the particles in the third and the fourthsub-regions for displaying the picture that will be absent in the thirdone and the fourth one of the substantially separate regions fordisplaying the subsequent picture are brought to their respectivereservoirs, and subsequently a second sub-transition wherein theparticles which are absent in the third and fourth sub-regions fordisplaying the picture that have to be present in the third and fourthsub-regions for displaying the subsequent picture are brought from theirrespective reservoirs to the third and/or the fourth sub-regions fordisplaying the subsequent picture.
 5. A display panel as claimed inclaim 1 characterized in that the pixel has a viewing surface for beingviewed by a viewer, the electrodes have substantially flat surfacesfacing the particles, and the surfaces are substantially parallel to theviewing surface.
 6. A display panel as claimed in claim 5 characterizedin that the surfaces of the electrodes are present in a substantiallyflat plane.
 7. A display panel as claimed in claim 1 characterized inthat the pixel has a viewing surface for being viewed by a viewer, theelectrodes have substantially flat surfaces facing the particles, thesurfaces of the electrodes being associated with sub-regions that aresubstantially contributing to the optical state of the pixel aresubstantially parallel to the viewing surface, and the surfaces of theelectrodes being associated with sub-regions that are substantiallynon-contributing to the optical state of the pixel are substantiallyperpendicular to the viewing surface.
 8. A display panel as claimed inclaim 1 characterized in that a first one of the sub-regions provides afirst reservoir for the first particles, a second one of the sub-regionsprovides a second reservoir for the second particles, and the displaypanel further comprises first decoupling means to reduce the influenceof the potential of the electrode associated with the first reservoir onthe position of the second particles.
 9. A display panel as claimed inclaim 8 characterized in that the display panel further comprises seconddecoupling means to reduce the influence of the potential of theelectrode associated with the second reservoir on the position of thefirst particles.
 10. A display panel as claimed in claim 9 characterizedin that the first and the second decoupling means are realized by theelectrophoretic medium comprising a hysteresis effect.
 11. A displaypanel as claimed in claim 9 characterized in that the first and thesecond decoupling means comprise a first and a second gate electrode forreceiving a first and a second gate potential, the first and the secondgate electrode being present between the electrodes associated with thefirst and the second reservoir.
 12. A display panel as claimed in claim11 characterized in that the first gate electrode is present between theelectrode associated with the first reservoir and the electrodeassociated with a third one of the sub-regions and the second gateelectrode is present between the electrode associated with the secondreservoir and the electrode associated with the third sub-region.
 13. Adisplay panel as claimed in claim 12 characterized in that , inoperation, the potentials of the electrodes associated with the firstand the second reservoir and the potential of the electrode associatedwith the third sub-region are substantially constant in time.
 14. Adisplay panel as claimed in claim 9 characterized in that the first andthe second decoupling means comprise a first particles repulsive layerpresent between the electrode associated with the first reservoir andthe electrode associated with a third sub-region, and a second particlesrepulsive layer present between the electrode associated with the secondreservoir and the electrode associated with the third sub-region.
 15. Adisplay panel as claimed in claim 9 characterized in that the first andthe second decoupling means comprise a first membrane through which apassage of the first particles is determined by a first threshold, thefirst membrane being present between the electrode associated with thefirst reservoir and the electrode associated with a third sub-region,and a second membrane through which a passage of the second particles isdetermined by a second threshold, the second membrane being presentbetween the electrode associated with the second reservoir and theelectrode associated with the third sub-region.
 16. A display devicecomprising the display panel as claimed in claim 1 and a circuitry toprovide image information to the display panel.
 17. The electrophoreticdisplay panel as claimed in claim 1 characterized in that said firstcharges particles have the same electric polarity as the second chargeparticles.
 18. Method of driving an electrophoretic display panel fordisplaying a picture and subsequently displaying a subsequent picture,the electrophoretic display panel comprising: a pixel having anelectrophoretic medium comprising first and second charged particles,the first charged particles having a first optical property, the secondcharged particles having a second optical property different from thefirst optical property, the first and the second charged particles beingable to occupy positions in a common region of the pixel, the commonregion comprising at least three substantially separate sub-regions, andan optical state depending on the positions of the particles in thecommon region; the method comprising controlling a transition of atleast a first number of the first particles and at least a second numberof the second particles in respective sub-regions in the common regionfor displaying the picture to separate sub-regions in the common regionfor displaying the subsequent picture, wherein the first number of thefirst particles and the second number of the second particles arecontrolled to always be in separate sub-regions during the transition,and wherein the transition comprises a sub-transition.
 19. The method asclaimed in claim 18 characterized in that said first charges particleshave the same electric polarity as the second charge particles.